*2.3.4 Effect of relative humidity*

Relative humidity has serious effect on drying rate and drying kinetic of banana fruits. Misha et al. [93] worked on the effect of humidity and temperature in the drying kinetics. They used drying temperature (45, 50 and 55°C) and relative humidity (10, 20 and 30%) variations at an air velocity of 1.0 m/s. They found that two-term model described the drying kinetics more accurately and then the rest of the models used in the experiment. They also found that the drying time was reduced as the temperature increased at constant air humidity. They observed that relative humidity of the air had an insignificant effect on the drying curve; this was attributed to the initial moisture content of the sample.

#### *2.3.5 Mass transfer parameters*

Drying process is used to prolong the storage or shelf life of banana products without changing the quality, structure and chemical properties. This is critically needed for quality of banana products and availability. The efficient and effective drying process could be obtained through an effective use of time, energy and cost [94]. This could also be seen in through speed and timely removal of moisture during the drying process. It has been established that moisture removal depends on the drying method and this will affect the technique of moisture movement towards evaporation for the drying process. Moisture movement is also effective moisture diffusivity and activation energy dependence [94].

#### *2.3.6 Effective moisture diffusivity*

Effective moisture diffusivity is defined as movement of moisture in banana products and is drying rate related [94, 95]. The difference between effective moisture diffusivity and drying rate is that effective moisture diffusivity is related to moisture velocity within the material, while the drying rate is the moisture vapourizing rate to air and depends directly on the pressure gradient that exists between material and the air due to a temperature gradient [94]. Effective moisture diffusivity is the parameter used to determine the drying rate of banana products and an indicator to determine an appropriate drying method that could be used to extend the banana product shelf life.

Also, according to Omolola et al. [87], effective moisture diffusivity is said to be a function of material moisture content and temperature, as well as of the material

structure [91]. Omolola et al. [87] in their work reported that the values of moisture diffusivities increased with increasing oven temperature. Similar observation was made by Aghbashlo et al. [95], Caglar et al. [96] and Doymaz and Ismail [97]. Omolola et al. [87] also reported that the disparities in moisture diffusivity values obtained in their study and the values reported for banana by Marinos-Kouris and Maroulis [98] and Thuwapanichayanan et al. [99] may be attributed to the effect of variety, geographical location, composition and tissue characteristics of the bananas.

#### *2.3.7 Activation energy*

Activation energy is energy needed to severe the moisture particles bonding for moisture movement in banana drying [94, 95]. Relationship between effective moisture diffusivity and activation energy is associated with drying characteristics and the effect of drying conditions on effective moisture diffusivity and activation energy of products [95, 100–102]. According to Xiao et al. [103], the activation energy, for a typical drying operation, ranges from 12.7 to 110 kJ/mol. Doymaz [104] reported the activation energy for drying banana slices to be 32.65 kJ/mol.

In determining activation energy, the Arrhenius equation is used in a modified form to illustrate the relationship between moisture diffusivity, mass transfer coefficient and ratio of drying process output power density to sample amount or the temperature for the calculation of the activation energy on the drying process [105, 106].

$$D\_m = D\_0 \exp\left(\frac{E\_{ad}m\_0}{P}\right) \tag{1}$$

$$H\_{m\text{-}aw} = h\_0 \exp\left(\frac{-E\_m m\_0}{P}\right) \tag{2}$$

#### **2.4 Quality aspects of dehydrated banana flour**

#### *2.4.1 Rehydration ratio*

Rehydration of banana slices depends on processing conditions, sample preparation, sample composition and extent of the structural and chemical disruption induced by drying [107]. Singh and Pandey [107] reported that the duration and severity of the drying process with the speed and degree of rehydration reflect faster and complete rehydration with decreased drying time. They opined that a minimization of shrinkage and the presence of well-defined intercellular voids show to promote increased rehydrating rate. Dried banana slices could be rehydrated at 25°C for 2 h by being immersed in 60 mL of distilled water. The rehydration ratio is described by:

$$Rr = \frac{m\_1 - m\_d}{m\_1} \tag{3}$$

**75**

processing.

*Banana Drying Kinetics*

*DOI: http://dx.doi.org/10.5772/intechopen.84669*

Δ*E* = ((*L*<sup>∗</sup>

*2.4.3 Bulk density and shrinkage*

weighing with a balance [110].

from the cells during dehydration.

photometer or a colorimeter before and after drying.

important quality parameter. L (lightness), a (redness) and b (yellowness) color values of the fresh and dehydrated banana slices can be measured using a spectral

> *<sup>d</sup>* − *a*<sup>∗</sup> *f*) <sup>2</sup> + (*b*<sup>∗</sup>

*H* = tan−1 (*b*/*a*) (5)

The bulk density is the ratio of the mass of banana slices to its total volume, and it can be determined by filling the slices in a cylinder of known volume and then

ρ<sup>b</sup> = m/V (6)

Shrinkage is an important change in the physical state of the product during drying which affects the quality of the final material, producing large alterations in its volume. Shrinkage can be expressed as ratio between the initial volume and the volume at a certain time after the moisture loss processes. Ramos et al. [111] reported shrinkage is the reduction of the product size which is a result of the reduction of its cellular dimensions of the product due to loss of moisture. According to Aguilera [112], shrinkage which occurs as a result agricultural produce drying is due to viscoelastic matrix contraction into the space previously filled by the water removed

*<sup>d</sup>* − *b*<sup>∗</sup> *f*) 2 ) 1/2

/*V*0) (7)

(4)

Total color change and hue angle could be calculated as follows:

*<sup>d</sup>* − *L*<sup>∗</sup> *f*) <sup>2</sup> + (*a*<sup>∗</sup>

Shrinkage of bulk banana slices could be represented by:

*2.4.4 Consumer perceptions/concerns and expectations about innovative and* 

Consumers around the world are better informed and educated as well as more demanding in their purchase preferences for quality health-promoting banana products. The banana industry has continued to search for innovative and novel technologies to provide safe, quality and stable banana products for human consumption. However, nonthermal processing technologies offer unprecedented opportunities and challenges for the banana industry to produce and market safe, high-quality health-promoting banana products. The research and development of nonthermal processing technologies for banana processing will provide an excellent balance between safety and minimal processing, as well as provide a balance between economic and quality requirements of the banana products [113]. Nonthermal banana processing is believed to be a new alternative to thermal banana

Currently, there are many nonthermal banana processing and preservation opportunities and challenges that need further research by the food industry. The advocates of nonthermal technologies rest their argument not only in the inactivation of microorganisms and enzymes but also in improving yield and development of foods with novel quality and nutritional characteristics [114, 116, 118]. Nonthermal processing could be effectively combined with thermal processing

Sh = (*V<sup>d</sup>*

*emerging banana processing technologies*

#### *2.4.2 Color measurement*

Color is a vital quality characteristic in dehydrated banana to nearly every consumer. It serves as an indicator of the intrinsic good qualities [108]. The relationship of color with consumer acceptability is common and inevitable [108]. It has been reported that drying operation changes the surface characteristics of foods and hence alters their reflectivity and color [109]. The color of food products is a very

*Banana Nutrition - Function and Processing Kinetics*

bananas.

*2.3.7 Activation energy*

*2.4.1 Rehydration ratio*

tion ratio is described by:

*2.4.2 Color measurement*

structure [91]. Omolola et al. [87] in their work reported that the values of moisture diffusivities increased with increasing oven temperature. Similar observation was made by Aghbashlo et al. [95], Caglar et al. [96] and Doymaz and Ismail [97]. Omolola et al. [87] also reported that the disparities in moisture diffusivity values obtained in their study and the values reported for banana by Marinos-Kouris and Maroulis [98] and Thuwapanichayanan et al. [99] may be attributed to the effect of variety, geographical location, composition and tissue characteristics of the

Activation energy is energy needed to severe the moisture particles bonding for moisture movement in banana drying [94, 95]. Relationship between effective moisture diffusivity and activation energy is associated with drying characteristics and the effect of drying conditions on effective moisture diffusivity and activation energy of products [95, 100–102]. According to Xiao et al. [103], the activation energy, for a typical drying operation, ranges from 12.7 to 110 kJ/mol. Doymaz [104] reported the activation energy for drying banana slices to be 32.65 kJ/mol.

In determining activation energy, the Arrhenius equation is used in a modified form to illustrate the relationship between moisture diffusivity, mass transfer coefficient and ratio of drying process output power density to sample amount or the temperature for

Rehydration of banana slices depends on processing conditions, sample preparation, sample composition and extent of the structural and chemical disruption induced by drying [107]. Singh and Pandey [107] reported that the duration and severity of the drying process with the speed and degree of rehydration reflect faster and complete rehydration with decreased drying time. They opined that a minimization of shrinkage and the presence of well-defined intercellular voids show to promote increased rehydrating rate. Dried banana slices could be rehydrated at 25°C for 2 h by being immersed in 60 mL of distilled water. The rehydra-

*m*<sup>1</sup> − *md*

Color is a vital quality characteristic in dehydrated banana to nearly every consumer. It serves as an indicator of the intrinsic good qualities [108]. The relationship of color with consumer acceptability is common and inevitable [108]. It has been reported that drying operation changes the surface characteristics of foods and hence alters their reflectivity and color [109]. The color of food products is a very

\_\_\_\_\_ *Eadm*<sup>0</sup>

> \_\_\_\_\_\_ −*Em m*<sup>0</sup>

*<sup>P</sup>* ) (1)

*<sup>P</sup>* ) (2)

*<sup>m</sup>*<sup>1</sup> (3)

the calculation of the activation energy on the drying process [105, 106].

*Dm* = *D*<sup>0</sup> exp(

*Hm*<sup>−</sup>*av* = *h*<sup>0</sup> exp(

**2.4 Quality aspects of dehydrated banana flour**

*Rr* = \_\_\_\_\_\_

**74**

important quality parameter. L (lightness), a (redness) and b (yellowness) color values of the fresh and dehydrated banana slices can be measured using a spectral photometer or a colorimeter before and after drying.

Total color change and hue angle could be calculated as follows:

$$
\Delta E = \left( \left( L^\*{}\_d - L^\*{}\_f \right)^2 + \left( a^\*{}\_d - a^\*{}\_f \right)^2 + \left( b^\*{}\_d - b^\*{}\_f \right)^2 \right)^{1/2} \tag{4}
$$

$$H = \tan^{-1} \text{ (}b/a\text{)}\tag{5}$$

## *2.4.3 Bulk density and shrinkage*

The bulk density is the ratio of the mass of banana slices to its total volume, and it can be determined by filling the slices in a cylinder of known volume and then weighing with a balance [110].

$$
\rho\_{\rm b} = \mathbf{m}/\mathbf{V} \tag{6}
$$

Shrinkage is an important change in the physical state of the product during drying which affects the quality of the final material, producing large alterations in its volume. Shrinkage can be expressed as ratio between the initial volume and the volume at a certain time after the moisture loss processes. Ramos et al. [111] reported shrinkage is the reduction of the product size which is a result of the reduction of its cellular dimensions of the product due to loss of moisture. According to Aguilera [112], shrinkage which occurs as a result agricultural produce drying is due to viscoelastic matrix contraction into the space previously filled by the water removed from the cells during dehydration.

Shrinkage of bulk banana slices could be represented by:

$$\mathbf{Sh} = \left(\mathbf{V}^d / \mathbf{V}\_0\right) \tag{7}$$

## *2.4.4 Consumer perceptions/concerns and expectations about innovative and emerging banana processing technologies*

Consumers around the world are better informed and educated as well as more demanding in their purchase preferences for quality health-promoting banana products. The banana industry has continued to search for innovative and novel technologies to provide safe, quality and stable banana products for human consumption. However, nonthermal processing technologies offer unprecedented opportunities and challenges for the banana industry to produce and market safe, high-quality health-promoting banana products. The research and development of nonthermal processing technologies for banana processing will provide an excellent balance between safety and minimal processing, as well as provide a balance between economic and quality requirements of the banana products [113]. Nonthermal banana processing is believed to be a new alternative to thermal banana processing.

Currently, there are many nonthermal banana processing and preservation opportunities and challenges that need further research by the food industry. The advocates of nonthermal technologies rest their argument not only in the inactivation of microorganisms and enzymes but also in improving yield and development of foods with novel quality and nutritional characteristics [114, 116, 118]. Nonthermal processing could be effectively combined with thermal processing

to provide improved banana safety and quality. Nonthermal processing has been found to facilitate the development of innovative banana products. Nonthermal technologies have been used to decontaminate, pasteurize and produce commercial sterilization of some banana products with good quality and excellent nutrient retention. The most important priority for future food science research will be the demand by consumers for technologies to meet consumer expectations with optimum-quality safe-processed banana. Zhang et al. [113] listed priorities and factors to consider when conducting research into novel nonthermal and thermal technologies for quality safe banana products as target microorganisms to provide safety, target enzymes to extend quality shelf life, maximization of potential synergistic effects, alteration of quality attributes, engineering aspects, reliability and economics of technologies and consumer perception of banana products from these technologies. They are of the opinion that the new technologies 'to process foods should be driven at maximizing safety, quality, convenience, costs, and consumer wellness' [115, 117–119].

#### *2.4.5 Glass transition on shrinkage in convective drying*

Several methods are employed for the preservation of banana products; drying is one of them. Drying is a heat and mass transfer process which removes moisture and thereby reduces the water activity of the banana products through vapourization or sublimation, which minimize enzymatic and microbiological reactions within the banana products. Several researchers have worked on drying and drying rate of different food materials. The drying rate has been found to depend on factors that influence the transfer mechanisms, such as the vapour pressure of the material and of the drying air, the temperature and air velocity, water diffusion in the material, the thickness and surface exposed for drying [120, 121].

Shrinkage of dried banana products is an important change in the physical state of the product during drying which affects the quality of the final material, producing large alterations in its volume. This phenomenon during drying is affected by glass transition. According to Roos [121], glass transition temperature (Tg) is the temperature at which an amorphous system changes from the glassy to the rubbery state. According to him in the glassy state, molecular mobility is extremely slow, due to the high viscosity of the matrix. Thus, the Tg can be taken as a reference parameter to characterize properties, quality, stability and safety of dried banana products [122].

Mayor and Sereno [123] and Bhandari and Howes [124] found that at most drying conditions, a significant amount of the dried product remains in the amorphous state, mainly due to insufficient time for crystallization to occur at the given drying condition. They observed that at rubbery state, shrinkage almost entirely compensates for moisture loss and changes in material volume are equal to the volume of removed water. However, it was observed that in food systems, shrinkage is rarely negligible, and it is advisable to take it into account when predicting moisture content profiles in the material undergoing dehydration [125–127].

#### *2.4.6 Optimization of drying conditions of bananas in tray dryer using response surface methodology*

Drying of banana products involves mass transfer phenomenon. Volume reduction or shrinkage occurs simultaneously during drying process, and it is an undesirable phenomenon in dried products. In general, reduction in volume is due to moisture transfer from dried banana products. This could be as a result of heat transfer into banana slices and mass transfer from the inside to the surroundings thereby causing unfavourable changes in dimensions and shape of the dried products [128, 129].

**77**

*Banana Drying Kinetics*

**3. Conclusions**

quality dried banana products.

There is no any conflict of interest.

**Conflict of interest**

*DOI: http://dx.doi.org/10.5772/intechopen.84669*

banana with reduced cooking time [132–134].

Response surface methodology (RSM) is a collection of statistical and mathematical techniques that has been successfully used for developing, improving and optimizing processes [129]. RSM enables a reduction in the number of experimental trials needed to evaluate multiple parameters and their interactions, thus requiring less time and labour. RSM has been widely applied for optimizing processes in the food industry [128–130]. It is used for product quality improvement in the drying process and has been widely used in new product development, as well as in the improvement of existing product design [130, 131]. There are already a number of studies on RSM applications in optimization of food processes that include optimization of banana production, processing parameter optimization for obtaining dry

This chapter showed that moisture content of banana fruits at harvest time is too high for storage and needs to be reduced. Drying characteristics, quality and mass transfer parameters for drying of banana slices were explained, and the process was discussed. It has been found that higher values of effective moisture diffusivity will accelerate moisture velocity within banana slices to achieve removal of moisture from produce for equilibrium moisture content at specific relative humidity. This will help in designing an effective drying method that will save time and energy consumption as well as cost to get good quality products. It was explained that Suzuki's model could be used to explain shrinkage during hot air drying process for banana slices. Shrinkage is a phenomenon and a significant alteration to be considered on quality of dried banana in food engineering applications. The use of this approach will be valuable to select proper drying conditions in order to obtain good

#### *Banana Drying Kinetics DOI: http://dx.doi.org/10.5772/intechopen.84669*

Response surface methodology (RSM) is a collection of statistical and mathematical techniques that has been successfully used for developing, improving and optimizing processes [129]. RSM enables a reduction in the number of experimental trials needed to evaluate multiple parameters and their interactions, thus requiring less time and labour. RSM has been widely applied for optimizing processes in the food industry [128–130]. It is used for product quality improvement in the drying process and has been widely used in new product development, as well as in the improvement of existing product design [130, 131]. There are already a number of studies on RSM applications in optimization of food processes that include optimization of banana production, processing parameter optimization for obtaining dry banana with reduced cooking time [132–134].
